There is an increasing demand for high-performance radio frequency (RF) front-end modules and components for use in applications such as, for example, advanced ground mobile radios. More particularly, it is becoming increasing necessary for devices such as advanced ground mobile radios to support various types of waveforms, including very high frequency (VHF) and ultra-high frequency (UHF) bands, which will require reconfigurable RF front-ends. One of the key challenges in developing such reconfigurable modules is to reduce the size and weight of the module while also supporting multiple communication standards.
One of the key components in RF front-ends is the RF bandpass filter. As such, the filter needs to satisfy requirements of multiple frequency band coverage and good RF performance, all in a small form factor. Various types of filters have been developed to attempt to adequately satisfy these requirements. For example, one type of filter is that based on CMOS technology. While CMOS-based filters offer a small size, the quality factor (Q) of the CMOS-based passive components that form the filter is low. The low Q of these components makes it hard to achieve a sufficiently low insertion loss for the filter unless Q enhancement techniques using active components are utilized.
Another type of filter that has been developed is that fabricated using micro-electromechanical system (MEMS) technology. More particularly, in one instance, a tunable bandpass filter designed in a second-order coupled resonator configuration has been developed. This particular filter was tuned using MEMS tunable capacitors that were employed in the resonator circuit or tank of the filter. However, in this implementation, a large-value fixed capacitor was placed in parallel with a smaller-value MEMS tunable capacitor to obtain the required capacitance value, which undesirably reduces the tuning range of the filter to less than 25%.
In other examples, switched capacitor banks with non-continuous digital tuning ranges were used to tune the frequency, and/or the bandwidth of the filter. The drawback of this approach is the low resolution of the digital tuning.
Thus, among other drawbacks of current implementations of continuously tunable filters, the tuning ranges thereof are limited by the tuning range(s) of the MEMS capacitors and inductive elements incorporated in the filter/resonator circuits thereof, and thus, they do not offer wide range tuning.
Accordingly, there is a need for RF front-ends and/or components thereof that meet requirements such as, for example, multiple frequency band coverage, continuous tuning, and good RF performance all in a small form factor, while also minimizing and/or eliminating one or more of the above-identified deficiencies.